Method of reducing coal ropes in a burner nozzle for pulverized coal

ABSTRACT

A coal nozzle for a burner on a pulverized coal fired furnace which includes an elongated tubular nozzle having an inlet for receiving a flowing stream of coal/air mixture and an outlet for discharging the flowing stream into a combustion zone of a furnace for combustion, and an inlet elbow connected to the inlet of the tubular nozzle. The interior outer surfaces of the elbow include a staircase surface configuration for engaging the incoming flowing stream whereby coal ropes in the stream are broken up for thereby improving flow distribution of the stream.

CROSS REFERENCE

This application is a division of U.S. application Ser. No. 12/322,468,filed 4 Feb. 2009.

BACKGROUND OF THE INVENTION

The present invention relates to a burner for pulverized coal and moreparticularly to a stationary coal nozzle for a burner on a pulverizedcoal fired furnace.

A wide variety of burner designs have been developed over the years forburners used in furnaces, boilers and the like for burning pulverizedcoal. Problems incurred in burning pulverized coal often can beassociated with coal roping in the fuel delivery system. Fuel roping isbelieved to be caused by centrifugal flow patterns established by elbowsand pipe bends.

Pulverized coal fired boilers have coal pipe networks which transportthe coal from the pulverizers to the individual burners using air as theconveying medium. For the specific case of a wall fired boiler, the lastturn in the coal/air mixture makes is a hard 90° turn in the burner.Coal roping is caused primarily by surface tension and pressuredifferentials within the coal pipes. The dense areas of coal flow orcoal ropes lead to poor flow distribution exiting the coal pipe andnozzle, which in turn has a negative effect on combustion.

Coal roping causes poor fuel distribution exiting the nozzle tip oroutlet which results in flame variations. These flame variations rangefrom substoichiometric fuel rich zones, where the reducing atmospherecontributes to slagging and water wall erosion, to high oxygen zones,which potentially create high thermal generation oxides of nitrogen.With these wide variations at each burner of a multiple burner unit,unit control is difficult. Accordingly, if the coal rope can beeffectively broken up, flow distribution at the exit of the coal pipesis greatly improved.

In an attempt to reduce nitrogen oxide levels and to reduce fuel roping,many stationary coal nozzles and nozzle tips have been developed overthe years. Many of them incorporate convergers and/or divergers. Forexample, see U.S. Pat. Nos. 4,348,170; 4,380,202; 4,479,442 and4,634,054. Others incorporate rib segments or dispersing devices withinthe coal nozzle which extend or protrude from the inside wall of thenozzle for distributing and diffusing a flowing stream of pulverizedcoal. For example, see U.S. Pat. No. 6,367,394 and U.S. Pat. No.6,105,516. All of these references have attempted to disrupt the coalroping flow into and out of the stationary coal nozzles with limitedsuccess.

It is accordingly a major object of the present invention to provide acoal nozzle design which provides effective breakup of coal ropes.

SUMMARY OF THE INVENTION

The coal nozzle of the present invention includes an elongated tubularnozzle having an inlet for receiving a flowing stream of coal/airmixture and an outlet for discharging the flowing stream into acombustion zone of a furnace for combustion. An inlet elbow is connectedto the inlet of the tubular nozzle.

In accordance with the teachings of the present invention, toeffectively eliminate coal roping, interior outer surfaces of the elbowinclude a sawtooth or staircase surface configuration for engaging theincoming flowing stream of coal/air whereby coal ropes in the stream arebroken up for thereby improving flow distribution of the stream.

Additional improvement in flow distribution is provided by including aplurality of annularly arranged and axially aligned fins in the tubularnozzle downstream of the elbow.

Conventional elbows used in coal nozzle burner configurations are eitherflatback elbows or lobsterback elbows. The flatback elbows have aremovable flatback cover plate with a flat interior surface and theconventional lobsterback elbows have a removable back cover plate with asegmented flat surface interior. With the flatback elbow, the staircasesurface configuration of the present invention is applied to theinterior surface of this removable cover plate. With the lobsterbackelbow, the staircase surface configuration is applied in staircasesegments to the respective interior flat segments of the removable back.The staircase surface configuration generally has spaces thereof whichare set at even intervals.

The staircase surface configuration is constructed of any suitable wearresistant durable material, such as steel or a ceramic, such as siliconecarbide.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages appear hereinafter in the followingdescription and claims. The accompanying drawings show, for the purposeof illustration, without limiting the invention or the appended claims,certain practical embodiments of the present invention wherein:

FIG. 1 is a view in partial vertical mid cross section of a stationarycoal nozzle of the prior art;

FIG. 2 is an enlarged perspective view in vertical mid cross section ofthe elbow and inlet portion of one embodiment of the coal nozzle of thepresent invention;

FIG. 3 is an enlarged view of one of the fins annularly distributed atthe inlet portion of the coal nozzle shown in FIG. 2;

FIG. 4 is a view from a different perspective of the elbow illustratedin FIG. 2 shown in partial segment;

FIG. 5 is a face view of the elbow shown in FIGS. 2 and 4 as seen alongsection line V-V in FIG. 2;

FIG. 6 is a perspective view in vertical mid cross section of the elbowand tubular nozzle combination of the present invention shown in a downflow configuration as opposed to the up flow configuration illustratedin FIG. 2;

FIG. 7 is a view in side elevation of a conventional prior artlobsterback elbow with the back removed and displaced;

FIG. 8 is a view in vertical mid cross section of the lobsterback elbowshown in

FIG. 7;

FIG. 9 is a face view in front elevation of a lobsterback elbowconverted and incorporating the principals of the present invention; and

FIG. 10 is a view in vertical mid cross section of the lobsterback elbowshown in

FIG. 9 and as seen along section line X-X.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a basic stationary coal nozzle 10 of the prior artis illustrated and includes an elongated tubular nozzle 11 having aninlet 12 for receiving a flowing stream of coal/air mixture as indicatedby the arrows, and an outlet 13 for discharging the flowing stream intoa combustion zone of a furnace for combustion.

Also included is an inlet elbow 14 connected to the inlet 12 of tubularnozzle 11. The flowing stream of coal/air mixture is provided from anupright supply pipe 15 from a conventional source (not shown).

The elbow 14 illustrated here is a conventional flatback elbow with aremovable flatback cover plate 16, which may be removed for wearreplacement and clean out. The tubular nozzle 11 is generally lined withceramic and may also include many types of deflectors or diffusers aspreviously described in the background. The elbow 14 and the cover plate16 are generally constructed of cast and machined carbon steel.

As previously discussed, elbow 14 induces the creation of coal ropes,which, as previously explained, are undesirable and need to beeliminated.

The elimination of coal ropes is accomplished by the embodiment of thepresent invention as illustrated in FIGS. 2 through 5.

In the embodiment of the present invention, interior outer surfaces 17of elbow 14, which in this instance is also the inside surface offlatback cover 16, are provided with a sawtooth or staircase surfaceconfiguration 18 for engaging the incoming flowing stream of thecoal/air mixture whereby coal ropes in the stream are broken up forthereby improving flow distribution of the stream.

This staircase surface configuration is attached or secured to theinterior outer surfaces 17 of elbow 14 by any conventional means, suchas machine screws 20. The staircase surface configuration 18 isconstructed of any suitable wear resistant material, such as steel orceramic, including silicone carbide.

The set of faces of alternating angles of the staircase configuration 18are more or less perpendicular and parallel to the incoming flow wherebythe faces which are somewhat perpendicular to the flow break up thedense coal rope. These faces are generally, but not necessarily, set ateven intervals and not in the same plane whereby they destroy the ropeand distribute it evenly throughout the tubular nozzle 11.

To supplement distribution enhancement, a set of fins 21 are set at evencircumferential intervals in the inlet 12 of tubular nozzle 11. Thelongitudinal edge of the fins 21 are parallel to the tubular nozzleaxis, and stand off of the inside diameter of the tubular nozzle 11 byapproximately 2 inches.

The entire inside of the tubular nozzle 11 is lined with ceramic blocks22 and fins 21 are also constructed of a wear resistant material, suchas steel or a ceramic, such as silicone carbide and the fins 1 aresecured to inside walls of tubular nozzle 11 by means of machine screwsinserted through passages 23, as best seen in FIG. 3.

The element 24 on the flatback cover plate 16 provides a conventionalclean out access and eye 25 provides a means for lifting the cover plate16 when it is removed from elbow 14.

The embodiment illustrated in FIG. 6 is for all practical purposesidentical to that illustrated in FIG. 2, except the elbow 14 is invertedfor a down flow configuration. The only difference is that a down flowdeflector 26 is provided at the inlet 12 of tubular nozzle 11 to deflectand redirect the stream of coal/air mixture upwardly back into the inlet12 for a more uniform distribution.

Instead of the conventional flatback elbow as shown at 14 in FIG. 1,another commonly used elbow in the industry is a lobsterback elbow asshown and illustrated in FIGS. 7 and 8. The primary difference is thatthe inside of the removable lobsterback cover plate 16 is provided witha series of flat segments 28. In a conventional lobsterback elbow theseinner flat segmented surfaces 28 are usually lined with a ceramic 30.

These flat surface segments 28 are positioned at the interior outersurfaces 17 of the elbow 14. For the purposes of breaking up coal ropesin accordance with the teachings of the present invention thelobsterback elbow 14 is adapted in accordance with the teachings of thepresent invention as shown in FIGS. 9 and 10 by the addition of astaircase surface configuration 30 similar to that illustrated in FIGS.2, 4, 5 and 6, except in this situation the configuration 30 is appliedas staircase segments 35 to the respective interior flat segments 28.These segments are attached by any conventional means, such as by anadhesive or by machine screws.

1. A method for reducing the occurrence of coal roping in pulverizedcoal fired boilers having a burner nozzle conveying a flowing stream ofcoal/air mixture, comprising: providing an elbow at an inlet for saidnozzle with interior outer surfaces thereof including a staircasesurface configuration; and conveying a stream of pulverized coal/airmixture through said elbow to said burner nozzle and thereby breaking upcoal ropes that occur in said stream.
 2. The method of claim 1,including the step of setting faces of said staircase surfaceconfiguration at even intervals.
 3. The method of claim 1, providing aplurality of annularly arranged and axially aligned fins in the nozzledownstream of said elbow and thereby enhancing the distribution of thestream flowing from said elbow.
 4. The method of claim 3, includingdeflecting and redirecting the stream of pulverized coal/air mixtureexiting said elbow inwardly into said nozzle prior to engaging saidfins.